N.M.R. and I.R. studies of 1, 1, 1 trifluoroacetone in proton donor solvents

Interactions of 1, 1, 1 trifluoroacetone with proton donor solvents of the type RH [where R=HO, CH₃S, CH₃CH₂CH₂CH₂S, CH₃O, (CH₃)₂N, (C₂H₅)₂N] have been investigated using NMR and infra-red techniques. Evidence of the formation of addition products of the type CF₃.C(OH)R.CH₃ where OH group is hydrogen-bonded with the fluorine of the CF₃ group has been obtained.     

Exploiting Coordination Isomerism for Controlled Self‐Assembly

We exploited the inherent geometrical isomerism of a Pt^II complex as a new tool to control supramolecular assembly processes. UV irradiation and careful selection of solvent, temperature, and concentration leads to tunable coordination isomerism, which in turn allows fully reversible switching between two distinct aggregate species (1D fibers?2D lamellae) with different photoresponsive behavior. Our findings not only broaden the scope of coordination isomerism, but also open up exciting possibilities for the development of novel stimuli‐responsive nanomaterials.     

Preparation,X-ray structure and reactivity of a stable glycosyl iodide

Highly selective reaction of methyl tetra-O-pivaloyl-beta-D-glucopyranuronate 2 with iodotrimethylsilane or (Me3Si)2 and I2 affords, in excellent yield, the 'disarmed' glycosyl iodide 1 which has good stability at 20 degrees C and excellent stability at 0 degrees C; the X-ray crystal structure of 1 is described, along with a comparison of its utility as a glycosyl donor to that of the corresponding bromide.     

Synthesis and Preliminary Screening of O-β-D-Galactopyranosides as Potential Mimic of UDP-Galp against Mycobacterium tuberculosis

O-Galactopyranosides were synthesized as potential mimics of uridine 5c-diphosphate galactopyranose (UDP-Galp), which is the substrate of the mutase enzyme involved in the mycobacterial cell wall biosynthesis by converting UDP-Galp to UDP-Galf. In vitro assay against the Mycobacterium tuberculosis H₃₇Rv strain gave promising results with minimum inhibitory concentration (MIC) values in the range of 3.13 to 25 μg/mL.     

Iodine and Its Interhalogen Compounds: Versatile Reagents in Carbohydrate Chemistry V. Synthesis of 1,2-trans-Linked 1-Thioglycosides from the Per-O-acetylated Glycoses 1 2

Abstract

Treatment of per-O-acetylated mono- and di-saccharides with (alkyl/arylthio)tri-methylsilane and iodine at ambient temperature results in the formation of the corresponding 1,2-trans-1-thioglycosides in very high yield. In the case of higher boiling thiols such as ethanethiol, the reaction can be effectively carried out in the presence of the thiol itself instead of the silylated derivative, but the reaction is not stereospecific. Moreover, in the latter reactions a portion of the starting material remains unchanged even on prolonged reaction. With β-D-glucose pentaacetate (11) as the starting material, its epimerisation occurred during the reaction and therefore the recovered starting material was of α-D-configuration. In addition, the methyl disulphide-hexamethyldisilane system has been found to serve as an effective and cheaper alternative to the expensive (methylthio)-trimethylsilane.

     

Effect of the Bulkiness of the End Functional Amide Groups on the Optical,Gelation, and Morphological Properties of Oligo(p‐phenylenevinylene) π‐Gelators

Herein, we describe the role of end functional groups in the self‐assembly of amide‐functionalized oligo(p‐phenylenevinylene) (OPV) gelators with different end‐groups. The interplay between hydrogen‐bonding and π‐stacking interactions was controlled by the bulkiness of the end functional groups, thereby resulting in aggregates of different types, which led to the gelation of a wide range of solvents. The variable‐temperature UV/Vis absorption and fluorescence spectroscopic features of gelators with small end‐groups revealed the formation of 1D H‐type aggregates in CHCl₃. However, under fast cooling in toluene, 1D H‐type aggregates were formed, whereas slow cooling resulted in 2D H‐type aggregates. OPV amide with bulky dendritic end‐group formed hydrogen‐bonded random aggregates in toluene and a morphology transition from vesicles into fibrous aggregates was observed in THF. Interestingly, the presence of bulky end‐group enhanced fluorescence in the xerogel state and aggregation in polar solvents. The difference between the aggregation properties of OPV amides with small and bulky end‐groups allowed the preparation of self‐assembled structures with distinct morphological and optical features.     

On single doping and co-doping of spray pyrolysed ZnO films: Structural, electrical and optical characterisation

In this paper we present studies on ZnO thin films (prepared using Chemical Spray pyrolysis (CSP) technique) doped in two different ways; in one set, ‘single doping’ using indium was done while in the second set, ‘co-doping’ using indium and fluorine was adopted. In the former case, effect of in-situ as well as ex-situ doping using In was analyzed. Structural (XRD studies), electrical (I-V measurements) and optical characterizations (through absorption, transmission and photoluminescence studies) of the films were done. XRD analysis showed that, for spray-deposited ZnO films, ex-situ doping using Indium resulted in preferred (0 0 2) plane orientation, while in-situ doping caused preferred orientation along (1 0 0), (0 0 2), (1 0 1) planes; however for higher percentage of in-situ doping, orientation of grains changed from (0 0 2) plane to (1 0 1) plane. The co-doped films had (0 0 2) and (1 0 1) planes. Lowest resistivity (2 × 10⁻³ Ω cm) was achieved for the films, doped with 1% Indium through in-situ method. Photoluminescence (PL) emissions of ex-situ doped and co-doped samples had two peaks; one was the ‘near band edge’ emission (NBE) and the other was the ‘blue-green’ emission. But interestingly the PL emission of in-situ doped samples exhibited only the ‘near band edge’ emission. Optical band gap of the films increased with doping percentage, in all cases of doping.